A black hole is a volume from which photons, or any matter, can not escape. More formally, the coordinate speed of light at the event horizon - the boundary of a black hole - is zero, as measured by a sufficiently separated observer.

learn more… | top users | synonyms

3
votes
2answers
774 views

How can we detect a black hole accurately?

I know there are many ways in detecting a black hole, but there are odds against them too. So I wanted to know a accurate method to detect a black hole. Here are the known methods to me and the odds ...
0
votes
0answers
30 views

Can we see the photon sphere from outside? [duplicate]

This question came to my mind when i saw the movie interstellar. In the movie there is a scene with a black hole and a sphere of light around it, what i assume to be the photon sphere. You can see it ...
0
votes
0answers
21 views

Do all stars Turn into Black Holes? [duplicate]

If all stars turn into black Holes one day, in far future, what will happen to Earth if Sun becomes a Black Hole.
3
votes
3answers
361 views

Definition of event horizon - Gravity around blackholes [closed]

Put simpler: A black hole is surrounded by a 'sphere' where, to an outside observer. the speed of light is (near) zero. What is the radius of that 'sphere' (for a non-rotating black hole) and how ...
1
vote
2answers
68 views

Possible paradox with black holes and time dilation [duplicate]

I am by no means an expert in the realm of physics. I do from time to time, try to understand the concepts of modern physics and their applications. I came across this video that I am currently ...
0
votes
2answers
57 views

How does a Black hole attract light? [duplicate]

Please no hate for lack of knowledge: I am somewhat fascinated with the subject of black holes. However, I do not understand a concept which is constantly attributed with black holes: that a black ...
3
votes
1answer
119 views

How long can a particle survive inside of the horizon of a black hole?

By examining the causal structure of a Schwarzschild black hole, one can see that a particle in region II is unable to escape to $r=\infty$. Such diagrams do not show, however, how long a particle ...
18
votes
0answers
276 views

How does one correctly interpret the behavior of the heat capacity of a charged black hole?

Consider the Reissner-Nordström metric $$ds^2=-f(r)dt^2+f^{-1}(r)dr^2-r^2d\Omega^2\hspace{2cm} f(r)=1-\frac{2M}{r}+\frac{M^2q^2}{r^2}$$ where I defined the charge-to-mass ratio $q:=Q/M$, which ...
0
votes
0answers
28 views

global transformations in 3d gravity

I am currently working on proper and improper gauge transformations in 3d gravity and btz black holes. (because I have seen it defined with many different ways I will just say that with "proper"and ...
2
votes
0answers
45 views

Are temperature and chemical potential of a black hole independent quantities?

I am a bit confused about the independent parameters in a charged black hole in AdS spaces. From equation (63) of this lecture notes we see that the temperature (T) of the black hole has chemical ...
0
votes
2answers
76 views

Black Hole Growth

When a black hole increases in size by engulfing matter, does this matter fall into the event horizon or does it just rotate around the accretion disk? EDIT: Clarified the beginning of the question. ...
0
votes
2answers
85 views

Do black holes violate the Uncertainty Principle?

If black holes have mass but no size, does that imply zero uncertainty in position? If so, what does that imply for uncertainty in momentum?
0
votes
0answers
36 views

Connection between Black Hole Firewalls and Hawking Radiation

In a previous post, I asked what constitutes a black hole firewall--namely, what is a possible mathematical description of the firewall. Now I have a new question, which is based around this guest ...
1
vote
3answers
51 views

Problem with black holes?

I understand that black holes are formed when supermassive stars (>10 times the size of our Sun) die. When they die, their cores continue to shrink. I have read that eventually the core reaches a ...
5
votes
1answer
268 views

What constitutes a blackhole firewall?

I understand that, to break the entanglement of two particles of Hawking radiation and therefore preserve monogamy of entanglement, there should be a firewall around the event horizon. This firewall ...
8
votes
2answers
1k views

Why don't electrons collaspe into black holes? [duplicate]

An electron has a mass of $9.10938291(40) \times 10^{−31} kg$. It also has a volume of $0 m^3$. This would imply it has infinite density. Shouldn't that make it collapse into a black hole? Why doesn't ...
1
vote
1answer
75 views

Can we observe a star collapse into a black hole? [duplicate]

Let's say that I happen by a star that has just burned out and is collasping into a black hole. I seat at infinity to watch it as a Schwarzschild observer. Will I ever see the black hole collapse into ...
3
votes
3answers
185 views

Size of black hole so large that I could pass event horizon without dying from tidal forces?

Were I to fall towards a typical black hole, the tidal forces would rip me apart well before I got to the event horizon. However, if a black hole were big enough, I could enter the event horizon ...
0
votes
1answer
60 views

Free-fall path into a black hole in Kruskal Coordinates

If an object at t=0 begins to free-fall into a black hole from X in Kruskal coordinates (https://en.wikipedia.org/wiki/Kruskal%E2%80%93Szekeres_coordinates), what does its path on the Kruskal-Szekeres ...
0
votes
1answer
45 views

Would infinite material cause a black hole?

If you have an infinite amount of any material(That doesn't have a critical mass to have nuclear reactions), would this matter form massive black holes that condense into an infinite black hole? Two ...
2
votes
0answers
58 views

Rigorous Proof of General Relativity's Non-renormalizability?

The answer to this question and the comments on it implies that general relativity has not been rigorously shown to be non-renormalizable for all loop diagrams -- only shown for two loops. However, ...
0
votes
0answers
23 views

How is the first law of black hole thermodynamics formulated for a non-vacuum solution with event horizon?

How is the first law of black hole thermodynamics formulated for a non-vacuum solution with event horizon?
2
votes
1answer
99 views

Black Hole surface area at Schwarzschild radius is half?

I have been interested in black holes for some time, and am still trying to wrap my head around some of their more obscure properties. Now I know that the Schwarzschild radius is $r= ...
0
votes
1answer
134 views

Any interesting implications of a holographic black hole in a holographic universe?

Bear with me; I don't have a background in physics, nor am I sure I even understand the things I'm talking about. I recently read that math/physics for a holographic black hole could be applied to ...
2
votes
0answers
39 views

Help me calculate the Euclidean action of a gravitating system!

I recently read Gibbons and Hawking's paper Action integrals and partition functions in quantum gravity, Phys. Rev. D 15 (1977) 2752. I am interested in repeating their calculations. It is fairly ...
0
votes
1answer
53 views

If a super massive black hole captures a very small black hole, would the smaller black hole be immune to spaghettification?

I think to answer this question we would have to fully understand the nature of black holes. It seems to me that the smaller black hole could have a lower density than the larger one. In this case the ...
0
votes
0answers
42 views

Does the uncertainty principle affect event horizons? [duplicate]

I was thinking about black holes. For a simple black hole the event horizon is given by a distance of 2 times mass (energy) of the black hole. (2m). But according to quantum mechanics, if you try to ...
0
votes
1answer
63 views

Wave equation on Schwarzschild background

I am trying to follow the solution of the wave equation for a scalar field on Schwarzschild background from http://batteringram.org/science/gr/scalar_wave.pdf. I have a problem on page 2 where they ...
0
votes
0answers
33 views

How can a singularity have infinite density? [duplicate]

I've heard many times that black holes have infinite density at their center, but I've also heard astronomers quote mass estimates for black holes. How could the singularity have infinite density if ...
0
votes
3answers
86 views

Path of light as it travels between two black holes

What would happen to light passing through a narrow space between the event horizons of two equal-mass black holes? Would it deviate or follow a straight path?
1
vote
0answers
81 views

Can tachyons escape the gravitational pull of a black hole?

Anything that crosses the event horizon of a black hole cannot escape the pull since it has crossed the Schwarzschild radius and thus, the escape velocity is greater than the speed of light, and since ...
7
votes
3answers
833 views

What is the radius of the event horizon?

I know that the Schwarzschild radius is given by $$r~=~\frac{2GM}{c^{2}}.\tag{1}$$ However, If we had the metric $$ds^2~=~−A(r,t)dt^2+\frac{dr^2}{B(r,t)}+r^2(dθ^2+\sin^2{θ}dϕ^2),\tag{2}$$ where ...
1
vote
2answers
155 views

How to derive the Schwarzschild radius? [duplicate]

I know that the Schwarzschild radius is given by $$r=\frac{2GM}{c^{2}}.$$ but I never seen a derivation for this equation. 1- Does anyone know how to derive this equation from general relativity? ...
0
votes
1answer
73 views

The age of black holes

I have a very small understanding of space-time however I have been watching some interviews and reading articles featuring theoretical physicist Kip Thorne and I have a few questions that I hope can ...
1
vote
0answers
78 views

Will a black hole cause scattering of a gravity wave?

In my GR textbook, it states that gravity waves can undergo interference but not scattering. I am just starting the chapter on linearised gravity concepts (weak field approximation) and my apologies ...
4
votes
4answers
384 views

“Center of a black hole is a time”

$\newcommand{\d}[1]{\mathrm{d} #1}$In one lecture (around 1:33:15) of the series of lectures "Theoretical Minimum" of Prof. Susskind he talks about black holes and the Schwarzschild metric: $$\d ...
2
votes
0answers
23 views

Nonsingularity of the Euclidean black hole metric

How can one show that the nonsingularity of the Euclidean black hole metric is required for thermal equilibrium of the original black hole in Lorentzian signature? It is mentioned in Prof. P. K. ...
2
votes
0answers
51 views

question about Blandford-Znajek original paper

I'm trying to follow the original Blandford-Znajek paper (found here), and I can't find how equations 2.1, 2.2 and 2.3 are obtained: 2.1 refers to "the charge density required to ensure that $E \cdot ...
0
votes
2answers
103 views

How can light enter a black hole if it cannot get out?

I have known for a very long time that light cannot exit a black hole. I can even understand some of the simpler reasonning about it, such as escape velocity, or space geometry inside the black hole. ...
2
votes
1answer
345 views

What happens to the total volume of a chunk of space that is being sucked into a black hole?

Does it increased, decrease, or stay the same? Maybe it explodes to infinity... Here is a similar question: Do black holes have infinite areas and volumes? But it's different because it asks how to ...
2
votes
2answers
298 views

How can we feel the effects of a Black Hole if all the mass is gone?

This question may help me learn more about the subtleties involved between the notions of gravity, in the Newtonian sense and those of curved spacetime, in the General Relativity sense. I will take ...
1
vote
1answer
50 views

Will the rotation of a neutron star prevent it becoming a Black Hole?

This question, to me anyways, is basically a balancing act between 2 possibly opposing effects. Take a neutron star with just too small a mass to overcome it's degeneracy pressure, failing to ...
1
vote
0answers
31 views

Magnetic dipole near black hole

Usually it is said that black holes cannot have electric or magnetic dipole, only electric charge and angular momentum are allowed quantities besides mass So, it would seem that black holes behave as ...
3
votes
1answer
76 views

Are moving objects producing stronger gravity fields? [duplicate]

If the strength of gravitational influence exerted by a body is derived from its mass and energy then is it true that a moving object which has some kinetic energy should also produce stronger ...
0
votes
0answers
30 views

Evaporation of black holes

What is the current scientific consensus about the evaporation of black holes? Is there any experimental evidence that support it? (I distinguish between Hawking radiation and black hole evaporation)
4
votes
4answers
111 views

Are there any planned experiments to intentionally create black holes in the lab for study?

And if they did what kind of machine would be making them? And what would they study?
1
vote
2answers
68 views

Does a body have to compress to its Schwarzschild radius to become a black hole?

When something is compressed to within its Schwarzschild radius, it will compress to a singularity within finite time regardless of what forces are involved. But is there some lesser point at which ...
0
votes
1answer
60 views

Difference between anti-matter and matter black holes [duplicate]

Laymen question: Is there any way to determine by observation whether or not a black hole has resulted from the core collapse supernova of a star originally composed of anti-matter versus a star ...
2
votes
1answer
87 views

Hawking Temperature of the BTZ Black Hole

The metric of the BTZ Black Hole is given by $$ ds^2 = - N^2 dt^2 + N^{-2} dr^2 +r^2(d\phi + N^\phi dt)^2 $$ with $$ N^2 = -M+ \frac{r^2}{l^2} + \frac{J^2}{4 r^2}, \ \ \ \ \ \ N^\phi = ...
3
votes
0answers
58 views

Charged black holes and AdS/CFT

People generalize the statements of AdS/CFT correspondence by adding black hole (charged black hole) in the gravity theory to provide the dual gauge theory finite temperature (finite density). I have ...